Heads up. I'm starting with a spoiler. One of the most effectively scary movie moments I’ve ever seen is in the otherwise unmemorable 1979 When A Stranger Calls. A young babysitter keeps getting phone calls asking “have you checked the children?” Eventually she tires of the prank and contacts the police. They tell her to make sure all the doors are locked and if it happens again to keep the stranger on the line. The next time he rings she manages to get a few more words out of him, but he still hangs up quickly. The police call back. "We’ve traced the call. It’s coming from inside the house”.

When I first heard that line some screamed, some jumped, and I yelled because my girlfriend at the time nearly pulled my arm off. What makes it so much more unnerving and disturbing than all the typical horror fare which follows is exactly what this month’s bidding blockbuster, The Host, has become the latest film to tap into. The enemy within.

Just like The Puppet Masters, David Cronenberg’s Shivers and many mostly B-movies, The Host centres on that sci-fi staple of an occupying organism which crawls onto - or more usually into – humans, taking near total control of them. But rather than this leading to a horrible transformation which is revealed, reviled and resisted over the course of the film, from the first frames of The Host we are in a future where the takeover is already almost complete. And where Earth seems all the better for it.

This makes it a neat variant both on invading life forms who want to eat us, or enslave us or just eliminate us, and on the cuddly ETs who just want to be our friends. Here the alien parasites, known as souls, have made the world a more joyous and harmonious place through the simple expedient of replacing our own natures with theirs, which by contrast are “compassionate, patient, honest, virtuous and full of love”. Wonderful, serene and wise as these souls (mostly) are, they only prosper by suppressing or snuffing out all those facets and flaws which makes each of us human. It’s smiley genocide.

Mind benders

If the idea of our species being enhanced by parasitic “souls” is ringing a distant bell, it might be that you’re reminded of Brian Aldiss’ 1962 novel Hothouse in which sentient fungi called morels boost our intelligence by attaching themselves to our heads. Either that or the many real world examples of parasitic behaviour that seem like they come straight from the movies.

There are viruses, flukes, wasps, tapeworms, fungi and a whole host of tiny creatures whose only goal in life is to infect, exploit and take control of their host’s every day behaviour.

Take grasshoppers infected with hairworm. One day they are going about their business; the next they find themselves compelled to jump into pools of water. The parasite essentially makes grasshoppers suicidal to ensure they can reproduce.

Then there is the gammarid – a tiny shrimp-like crustacean that are a favourite of the thorny-headed worm. Your normal, uninfected gammarid is a shy creature that when threatened with being eaten, will dive into the mud at the bottom of the pond they live. But once infected, the creature does the opposite – shooting towards the surface. Again, the host has taken control of its senses – turning the gammarid into a zombie and allowing it to complete its life cycle by being eaten by a bird.

Or there is the Lancet liver fluke, an ingenious creature that goes from cow, to snail to ant and back again – the really clever bit coming at the end of the life cycle where the mind bending creature forces the unwitting ants to climb to the top of a blade of grass night after night, until it is eaten by a cow, starting the whole cycle again.

Love drug

And behaviour bending may also happen closer to home. Several studies have shown over the years that we too may be under the influence. With a stress on the “may”.

It has been known for a long time that rats infected with the single-celled brain parasite Toxoplasma gondii – commonly found everywhere from soil, infected meat and cat faeces – causes them to lose their fear. Stick an infected rat in a room with a cat and it will carry on oblivious to its inevitable fate.

And humans - of which a third may be infected with Toxoplasma gondii - could have similar tendencies (to lose their fear, rather than to sit happily in a room with a cat). A 2006 study, for example, suggested the infection could cause subtle but significant personality changes – potentially affecting everything from guilt, intelligence and affection. The author even raises the question of whether the creature has influenced human culture.

Which brings us back to The Host. There is a bit more to the film than just parasitic performance, and – being based on a novel by Stephenie “Twilight” Meyer – there’s also room for oodles of complicated romantic geometry way beyond bizarre love triangles, with people and their souls falling collectively or separately for other people and/or their souls. I said it was complicated.

Had The Host been made a few decades ago, it might have been taken as a thinly veiled parable about the threat of communism: a poor cousin to that greatest of alien invasion movies, the original 1956 Invasion of the Bodysnatchers (which, for the record, all those involved with have always insisted was just a thriller, nothing more). Nowadays, although Meyer herself claims a key theme is learning to love the bodies we are in, some have viewed The Host as echoing contemporary concerns about the over use of drugs that may calm us down or cheer us up, but subdue our personalities as well as our anxieties. Others see it as being about mental disease and decay, and the fear that our self slips away from our body. And that’s all before – at the time of writing – the film has even been released.

Even in the hands of Andrew Niccol, the writer/director responsible for such thought-provoking science fiction as Gattaca and The Truman Show (and more recently but less effectively In Time) I’m not sure that The Host is able to bear the weight of all those possibilities. It is mostly just a teen-friendly sci-fi romance with a love conquers all message. But perhaps all these interpretations and extrapolations reveal another parasitic relationship, the one in which different audiences burrow into movies and find what they need to feed off within them.

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